noun
both houses of parliament; both houses of the Diet
Refers specifically to the two chambers of Japan's National Diet: the House of Representatives (衆議院) and the House of Councillors (参議院).
法案は両議院で可決された。
The bill was passed by both houses of the Diet.
The upper house (House of Councillors). 両議院 includes this and 衆議院.
Compound of 両 (both) + 議院 (parliamentary house).